In most imaging apparatuses, for example, digital still cameras, an optical finder is included. In recent years, in technological fields of digital still cameras, the development of optical finders has progressed towards the direction of small sized, longer focal point devices. Optical finders of the digital still cameras include optical finders of a TTL format in which a photogenic subject image based on light passing through an imaging lens system is viewed and optical finders of a format other than the TTL format.
Optical finders other than the TTL format are difficult to realize a structure that fits into a small sized body and corresponds to a long focal point. Therefore, digital still cameras not including an optical finder and digital still cameras including an electrical viewfinder (referred to as EVF hereinbelow) are increasing.
Digital still cameras of this kind include an image pickup device that takes an image of a photogenic subject, an image pickup device drive part that drives the image pickup device in order to read out image data from the image pickup device and a digital signal processing part in which image data outputted from the image pickup device is inputted and processed.
In addition, it is known that digital still cameras include one image display part connected to the digital signal processing part and configured to display using one display format of processed image data, another image display part connected to the digital signal processing part and configured to display using another display format of the processed image data and requiring more processing time than that required for display processing by the one display format, an image switch-over part for switching over an image display device between the one image display part and the other image display part and a clock signal supply part that sets the speed of operation of the image pickup device drive part.
For example, it is known that an imaging apparatus, for example, a digital still camera includes an image display part, for example, an electrical viewfinder (referred to as EVF hereinbelow) and a liquid crystal display device (referred to as LCD hereinbelow) (For example, refer to JP2004-15595A).
In this digital still camera, when a user performs photographing manipulation whilst visually confirming a real-time image of a photogenic subject, a frame rate at the time an image is displayed on the EVF or the LCD in live view is set to be a standard frame rate.
In addition, when a user does not perform photographing manipulation whilst visually confirming a real-time image of a photogenic subject, the frame rate at the time an image is displayed on the EVF or the LCD in live view is set to be a frame rate lower than the standard frame rate.
Furthermore, in this digital still camera, the frame rate is lowered based on detection results by a battery detection circuit and the frame rate is lowered corresponding to the exposure time of an image pickup device, for example, a CCD.
By these processings, this digital still camera has a decreased amount of electricity consumption per unit time and the burden on a processing circuit built-in the digital still camera with regard to image processing is eased.
As a result, the battery can be effectively utilized and as many images as possible can be recorded and stored.
In addition, for example, a digital camera is known having a constitution of recognizing by a CPU (central processing unit) an output impedance characteristic value of a power source and a large consumption electrical current operation mode, when the output impedance characteristic value of the power source exceeds a standard value and during the large consumption electrical current operation mode time span, a drive frequency of a CCD is set to be lower than the ordinary frequency, and when the output impedance characteristic value of the power source is below the standard value, a drive frequency of a CCD at the time obtaining an AF evaluated value is set to be higher than the ordinary frequency (for example, refer to JP3983126B).
In this digital still camera, when the output impedance characteristic value of the power source exceeds a standard value and during the large consumption electrical current operation mode time span, because a drive frequency of a CCD is set to be lower than the ordinary frequency, a high quality image can be stably obtained. In addition, when the output impedance characteristic value of the power source is below the standard value, because a drive frequency of a CCD is set to be higher than the ordinary frequency at the time an AF evaluated value is obtained, obtaining of the AF evaluated value is performed at high speed so that the total imaging time can be shortened.
Incidentally, in the case an EVF is compared with a conventional LCD, the problems described hereinbelow are present.
FIG. 1 illustrates an external view of a digital camera 1 including an image display part, for example, an EVF 2. The EVF 2, as illustrated in FIG. 2, is approximately constituted by a display device, for example, a small sized LCD 3, a magnifying lens optical system 4 and a cover member 5 of a tube shape that covers these and shields light.
Comparing this EVF 2 when used for monitoring with an image display part, for example, an LCD conventionally used for confirmation of framing and viewing photographed images in a digital still camera, the LCD 3 of the EVF 2 has a display screen size smaller than a conventional LCD display screen size so that it is easy to view across the whole screen.
In addition, because the LCD 3 and the magnifying lens optical system 4 of the EVF 2 are covered by the cover member 5, outdoor visibility is improved in comparison to a conventional LCD.
Although the EVF 2 has the above-described merits, structurally, it has an inclination to be compared to an optical finder that generates no output delay. That is, because the EVF 2 has a small display screen size, a user has to stare at a small screen area and this is problematic as the movement of a photogenic subject on the screen causes misalignment against the actual movement of the photogenic subject (speed of follow-up).
In addition, in the case where outdoor photographing is performed using a digital still camera, smearing, which is not problematic when monitoring is performed using a conventional LCD, is likely to become a problem in the case of the EVF 2.
The smearing thereof is said to be generated as if dragging on a thin trail across a broad area of the whole screen in the case where a high brightness photogenic subject exists within a photographing frame.
In the case of performing outdoor photographing using a digital still camera and in the case of using a conventional LCD to perform monitoring, in the conventional LCD, because visual confirmation is originally performed under an unfavorable condition in which visibility is not good, such smearing was virtually not a problem.
In comparison, in the EVF 2, the LCD 3 is visually confirmed in a state shielding light whereby in comparison to a conventional LCD, visual confirmation is performed under a better condition in which visibility is good so that the smearing becomes eye-catching.
In addition, when a user performs monitoring using the EVF 2, the user feels a sense of discomfort from the smearing generated due to the bright spot of a spotlight and an indoor fluorescent lamp, which is not generated in an optical finder
In this way, a digital still camera including the EVF 2 differs from a conventional LCD in that the EVF 2 is used as a substitute for an optical finder, and has unique problems.
In addition, depending on the types of output device for image data, there are digital still cameras in which it is necessary to convert the display format from general video formats (for example, video formats of a CCIR-601 format, a CCIR-656 format and a 8 bit RGB serial format) to a video format for displaying on the actual display device, for example, an LCD.
A display device of the EVF 2, for example, an LCD 3 comprised from ferroelectric liquid crystal is used. Image data outputted from an output device in a general video format must be converted into RGB surface sequence data using an encoder circuit within the LCD 3.
In the case this LCD 3 comprised from ferroelectric liquid crystal is used, in comparison to an LCD of a display format that does not require the conversion of video format, a delay of about one sixtieth of a second is generated from the photographing time point to the display time point in which a photogenic subject image is displayed on the screen of LCD 3.
Hereby a constitution for converting the video format of image data using an encoder circuit within the LCD 3 is adopted, but a delay is also generated in the case where video format is converted in an image processing part of a digital still camera.
Furthermore, a conventional LCD and the LCD 3 used in the EVF 2 differ in their power consumption. In general, power consumption of display devices differs. For example, in the case of an LCD using an LED as a light source, in order to allow the brightness per unit area to be constant, it is clear that the larger the image display area, the larger the power consumption.
Because the power consumed at the display device takes up about one fourth of the total power consumption of an imaging apparatus, if the power consumed at the display device changes, the change influences the total power consumption of the imaging apparatus in no small measure.
When the power consumption of a digital still camera changes due to the switch-over of image display parts to which image data is outputted, a setup value of a battery check voltage set based on a discharge curve property of a battery under one condition must be changed according to display devices used as output devices.
That is, even when the residual quantity of battery is the same, if the power consumed by an image display part becomes less, then the lessened portion becomes the extra portion of power that can be distributed to photographing and as a result, a greater number of pieces of a photographed image can be obtained. On the contrary, even when the residual quantity of battery is the same, if the power consumed by an image display part increases, then the increased portion becomes the portion of power that cannot be distributed to photographing and as a result, the number of pieces of images that can be photographed is decreased.
In this way, the setup value of a battery check voltage used to indicate based on the residual quantity of battery how many remaining pieces of images can be photographed is changed according to the types of display devices used as output devices of image data so that a user is notified about the appropriate number of pieces that can be photographed.
However, in this way, set up values are changed for each difference in power consumption properties of image display parts of output devices, a memory of the disposed number of image display parts with differing power consumption properties is prepared and it is necessary to record and store the setup value in this memory, which leads to growth of memory capacity and consequently, the cost of the digital still camera is increased.
Therefore, in an imaging device able to switch-over between an image display part in which together with delay, smearing is crucial and becomes a problem but power consumption is less and an image display part in which together with delay, smearing is not crucial and does not become a problem but power consumption is large, the property of the imaging apparatus as a whole changes according to a display device used for monitoring.